1. Field of the Invention
The present invention relates to a resist top coat composition for forming a top coat on a photoresist film for the purpose of protecting the photoresist film in photolithography for micropatterning processes in manufacturing processes of semiconductor devices and so on, for example, in the liquid immersion photolithography in which ArF excimer laser having a wavelength of 193 nm is used as a light source and liquid such as water is inserted in a gap between a projection lens and a substrate; and to a patterning process using the resist top coat composition.
2. Description of the Related Art
There has been increasingly achieved a finer pattern rule along with a tendency in which integration and speed of LSIs have become higher in recent years. This is based on use of shorter wavelength exposure light sources. For example, use of a shorter wavelength of KrF excimer laser (248 nm) instead of i line (365 nm) of a mercury-vapor lamp has allowed mass production of a 64 M bit (a processing dimension of 0.25 μm or less) DRAM (dynamic random access memory).
Furthermore, in order to manufacture DRAM with an integration of 256M, 1 G or more, the lithography using ArF excimer laser (193 nm) has been earnestly examined, and fabrication of 65 nm node devices has been examined with combination of ArF lithography and a lens having an enhanced NA of 0.9 or higher.
As for fabrication of the next 45 nm node devices, use of F2 laser having a wavelength of 157 nm was suggested to be a possible choice. However, introduction of F2 lithography has been postponed due to many problems represented by a detriment in cost, underperforming resists, and the like. And then as an alternative of the F2 lithography, ArF liquid immersion lithography has been suggested. And the ArF liquid immersion lithography has been developed for the purpose of early introduction of it (See Proc. SPIE Vol. 4690(2002) xxix).
In the ArF liquid immersion lithography, a gap between a projection lens and a wafer is filled with liquid such as water, ArF excimer laser is irradiated via the liquid. Water has an index of refraction of 1.44 with 193 nm light, and a pattern can be formed even with using a lens having an NA of 1.0 or more. In theory, NA can be increased up to 1.44. Resolution is enhanced by increment of NA. It is suggested that combination of a lens having an NA of 1.2 or more and ultra resolution techniques may realize fabrication of 45 nm node devices (See Proc. SPIE Vol. 5040 (2003) p 724).
However, conducting exposure with the presence of water on a photoresist film causes leaching of a part of generated acid and a basic compound added to the resist film to the water layer. As a result, this can cause pattern deformation or pattern collapse. In addition, it has also been pointed out that small amounts of water droplets remaining on the resist film can penetrate the resist film to cause defects. In order to solve the above-mentioned drawbacks, it has been suggested that in the ArF liquid immersion lithography, a top coat is placed between the resist film and water (For example, see 2nd Immersion Work Shop: Resist and Cover Material Investigation for Immersion Lithography (2003)).
The top coat that is formed on a photoresist film has been investigated as an antireflection film represented by the ARCOR (antireflective coating on resist) method (For example, see Japanese Unexamined Patent Application Publication No. 62-62520, No. 62-62521, and No. 60-38821). The ARCOR method includes a step of forming a transparent antireflective coating on a photoresist film and removing the antireflective coating after exposure. In this case, use of compositions having a low refractive index such as perfluoro alkyl polyethers or perfluoro alkyl amines as a resist top coat composition reduces remarkably reflection at the photoresist film/resist top coat interface, thereby enhancing dimensional accuracy. Then as examples of such a resist top coat composition, there has been suggested amorphous polymers such as perfluoro (2,2-dimethyl-1,3-dioxol)-tetrafluoroethylene copolymer (For example, see Japanese Unexamined Patent Application Publication No. 05-74700).
However, such fluorine-containing compounds have a low compatibility with organic compounds, and flon solvents are used for applying and stripping top coats, thereby having major drawbacks in terms of environment and cost.
Other than the above resist top coat compositions, applications of water-soluble or alkali-soluble compositions have been examined (For example, see Japanese Unexamined Patent Application Publication No. 06-273926, Japanese Patent Publication No. 2803549, and J. Photopolymer Sci. and Technol. Vol. 18, No. 5 p. 615 (2005)).
However, water-soluble top coats cannot be used for the ArF liquid immersion lithography because liquid such as water overlies a top coat. On the other hand, alkali-soluble resist top coat compositions have a major advantage in terms of cost because the compositions are strippable with alkaline developers and no additional installation of a unit for stripping the top coat is required. Based on the above-mentioned viewpoints, water-insoluble and alkali-soluble resist top coat compositions have been earnestly developed. For example, there has been suggested a resist top coat composition using a methacrylate resin having a fluorine-containing alcohol in a side chain.
As for properties required for resist top coat compositions, there are not only a property to prevent leaching of a generated acid or a basic compound in a photoresist film into water but also water repellent property and water-sliding property. Among these properties, it has been reported that the water repellent property is effectively enhanced by introducing fluorine to a resin, and that the water-sliding property is effectively enhanced by forming micro domain structures in combination of different water repellent groups (For example, see XXIV FATIPEC Congress Book, Vol. B, p. 15(1997); and Progress in Organic Coatings, 31, p. 97 (1997)).
By the way, in the above cases, there can occur problems depending on the types of photoresist films that when a resist top coat is formed on a photoresist film, film loss occurs in the surface portions of developed photoresist film and the photoresist film has a rounded top shape. In this case, rectangular and excellent resist patterns cannot be obtained. Therefore, there has been demanded a resist top coat composition that more certainly provides rectangular and excellent resist patterns.